IME, one of the issues with internal routing is the micro housing/sleeve that encases the cable going through the interior of the frame has a tendency to get kinks in it. I have one bike that has internal routing, I finally got it to shift correctly after re-doing all the cables and housing, using a sleeve for the cable that is a bit more flexible, black replaced white/clear, making sure the cable/housing was lightly lubed with oil, and minimizing the angles in the routing. I am positive that the routing was poorly done by the shop the bike was purchased from. I bought the bike online from a shop 3,000 miles away, so having them do the re-routing was not an option. I did buy a Park Tool routing tool kit, and it helped, but I am pretty sure it can be done without it.

For transparency, I was not at all familiar with interior routing and it took me quite a while to get tired of constant adjustment of the shifting. Between watching videos and my LBS, they gave me the different sleeve, the re-routing was a success and I have had no more shifting issues since. This is a CF frameset, and do still get some low level rattling from the cables going through the down tube. I am not in the market for a bike, but I likely would not get another with internal routing.

This was a 2014 model that I purchased new in 2016. From what I have read and seen, the performance of this routing has been considerably improved.